1. Field of the Invention
The present invention relates to a fixing device that is provided in an image forming apparatus such as a copy machine, printer or facsimile and fixes a toner image onto a sheet by using a heated member heated by induction heating of a coil, and particularly to a cooling mechanism of an image forming apparatus that prevents temperature rise of the coil.
2. Description of the Related Art
Recently, there has been an induction-heating fixing device used in an image forming apparatus such as an electrophotographic copy machine or printer. In this induction-heating fixing device, when the temperature of a coil in the induction heating device has risen and exceeded the Curie point, induction heating performance is lowered. When the temperature of the coil has exceeded the heat-resistance temperature of the insulating coating of a conductor wire, a safety problem occurs. Therefore, there has conventionally been a device to prevent temperature rise in the induction heating devise used in the fixing device. As such a fixing device, for example, JP-A-2004-45717 discloses a fixing device in which a radiation hole is formed in a housing of an induction heating unit, thus radiating heat that is emitted from a supporting frame, an induction heating device, a C-coil core and the like.
However, the conventional device is not suitable to cool a specific area in the induction heating device though it is possible to uniformly cool the entire area of the induction heating device. Meanwhile, there is an induction heating device in which the ends of a coil are substantially bent so as to compensate for the insufficient quantity of heat due to reduction of the magnetic field at the coil ends, or the insufficient quantity of heat due to reduction of the magnetic field in neighboring parts of a coil divided into plural parts. Thus, the length of the coil in the induction heating device is made as short as possible.
However, in the case where the ends are bent in this manner, temperature tends to rise more greatly and be higher at the bent parts of the coil than its other parts that are not bent. In the induction heating device using the coil with its ends bent in this manner, the bent parts cannot be efficiently cooled even when the entire device is cooled. As a result, reduction in induction heating performance or peeling of the coating of the conductor wire due to the temperature rise at the bent parts may occur.
Thus, in order to overcome the insufficient quantity of heat in the fixing device, even in the case where the coil ends in the induction heating device are bent, temperature at the bent parts of the coil is to be prevented from rising. It is desired that a cooling mechanism of a fixing device should be developed to realize a high-performance fixing device in which fixing failure due to the insufficient quantity of heat does not occur and in which temperature rise at the coil ends is prevented to achieve high induction heating performance and the coating of the conductor wire will not be peeled, thus maintaining safety.